# EXAMPLE 5 Find permutations of n objects taken r at a time Music You are burning a demo CD for your band. Your band has 12 songs stored on your computer.

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EXAMPLE 5 Find permutations of n objects taken r at a time Music You are burning a demo CD for your band. Your band has 12 songs stored on your computer. However, you want to put only 4 songs on the demo CD. In how many orders can you burn 4 of the 12 songs onto the CD? SOLUTION Find the number of permutations of 12 objects taken 4 at a time. ( 12 – 4 )! 12 P 4 = 12! = 11,800= 12! 8! 479,001,600 40320 = ANSWER You can burn 4 of the 12 songs in 11,880 different orders.

GUIDED PRACTICE for Example 5 Find the number of permutations. 5P35P3 4. ( 5 – 3 )! 5P35P3 = 5!5! = 60= 5 4 3 2 1 2 1 SOLUTION = 60 ANSWER SOLUTION = 4 ANSWER 5. 4P14P1 ( 4 – 1 )! 4P14P1 = 4!4! = 4 = 4 3 2 1 2 1

GUIDED PRACTICE for Example 5 Find the number of permutations. 6. 8P58P5 ( 8 – 5 )! 8P58P5 = 8!8! SOLUTION = 6720 ANSWER = 6720= 8 7 6 5 4 3 2 1 3 2 1

GUIDED PRACTICE for Example 5 Find the number of permutations. 7. 12 P 7 = 3,991,680 ANSWER ( 12 – 7 )! 12 P 7 = 12! SOLUTION = 3,991,680 = 5 4 3 2 1 12 11 10 9 8 7 6 5 4 3 2 1

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